Changi is very easy to get in and out, immi wise, out of the airport that is.
They have gotten rid of a lot of their travel restrictions, and even if you have to go out into the open area, 9 hours is enough to go out and come back into the airport secure zone.
ICA is also a shortish process, depending on your passport issuing country/nationality, usually no visa, so its easy.
Airport security scanning there of hand luggage takes place at the gate, so if you do get a BP at a transfer desk, you will go through security at the next gate for your flight, not like in Aust int airport, where they security scan everyone at one point, at Changi, they scan each plane's set of pax just before the pax enters the dep gate.
If you have to go out into the open zone, you can go to the KLM desk at SIN, or do OLCI, but do go to the desk to get papery BP, as you need this to get past the first scanning point, where an officer will check all boarding passes, to make sure only pax get past that first screening point.
I don't think QF check in at your first port of int departure will give/issue you the KLM BP, so you can try OLCI on the KLM website, if OLCI can be done 48 hours prior to flight, (if allowed before KLM flight).
If you can't do OLCI, try transfer desk at Changi in the secure zone.
If all else fails, claim bags, to out, get paper BP and come back in.
Edit: if all goes well, KLM website says you can do OLCI 30 hours before flight.